The present invention relates generally to monovinylarene-conjugated diene block copolymers adapted for shrinkable film applications.
Monovinylarene-conjugated diene block copolymers are increasingly used in shrinkable film applications. Typically, a film is “oriented”, i.e., stretched, at an “orientation” temperature high enough to allow it to be stretched to a film of desired thickness without breaking. As an example, orientation temperatures are generally less than 100° C., and films having a thickness of 2 mil are common.
The film should generally retain its stretched orientation at ambient temperatures, thus avoiding “natural shrinkage” during storage. A common specification for natural shrinkage is that a film should not shrink more than 5% when stored at 40° C. for 7 days. In the context of shrink films, percent shrinkage refers to the change in dimension of an oriented film compared to its oriented shape. Upon application, the film can be shrunk around an object at an elevated “activation” temperature, which can be around 100° C., as an example.
It is generally desirable that a shrink film be substantially clear. A common specification in such cases is that a film should have a haze of less than 5% (BYK Gardner Haze-Gard Plus according to ASTM D-1003 (1992) using test specimens of 2 mil thickness).
There is a continuing need for compositions and methods directed at achieving objectives including the foregoing, particularly in a cost efficient manner.